The world-wide variation in the incidence of colon cancer and the increased incidence found in migrants from low to high risk areas support the notion that environmental factors are involved in the etiology of this disease. These environmental factors are thought to be largely dietary. Furthermore, it has been hypothesized that intestinal bacteria may be generating carcinogens or co-carcinogens from bile acid substrates. The overall objective of this proposed research is to delineate the role of bile acids and the intestinal microflora in colon cancer carcinogens from bile acid substrates. The overall objective of this proposed research is to delineate the role of bile acids and the intestinal microflora in colon cancer carcinogenesis. The initial goal will be to determine if intestinal bacteria having 7-alpha-dehydroxylase activity produce chemical mutagens (carcinogens) by the Ames et al. (43,44) assay when cultured in different media with and without bile acid substrates. The second goal will be to determine the concentraion of chemical mutagens (carcinogens) in extracted feces taken from individuals with different levels of 7-alpha-dehydroxylase activity, i.e., colon cancer patients (high levels), alcoholic cirrhosis patients (low levels), and control individuals (intermediate levels). Moreover, beta-glucuronidase (beta-glu), azoreductase (azr), and nitroreductase (nr) specific activities will be determined spectrophotometrically in fecal extracts prepared from these 3 groups. The third goal will be to determine radiochromatographically the distribution of 7-alpha-dehydroxylase in different intestinal Clostridium ssp. and to determine the specific activities of (beta-glu), (azr) and (nr) in cell extracts prepared from these bacteria and control (non 7-alpha-dehydroxylating) intestinal bacteria. The fourth goal will be to purify and characterize by conventional biochemical techniques 7-alpha-dehydroxylase from Clostridium leptum and to determine if this is but one enzyme in a bile acid catabolic pathway in this organism. The final goal will be to show the 7-alpha-dehydroxylation reaction in C. leptum is coupled to energy transformation processes of the bacterial cytoplasmic membrane using selective metabolic inhibitors and membrane vesicles.